The IFN consensus sequence binding protein (ICSBP/IRF-8), which belongs to the interferon regulatory factor family of transcription factors, is essential for a Thl immune response. ICSBP plays an important role in the host defense against microbial pathogens, but the exact roles of ICSBP in inflammation and chronic inflammatory diseases are still not clear. IL-10-/- mice, which develop colitis characterized by increased Thl cytokines, mimic many aspects of human Crohn's disease (CD). The importance of ICSBP in the development of colitis is shown by the lack of disease in ICSBP and IL-10 double knockout mice. In addition, ICSBP mRNA and protein are highly expressed in the colons of IL-10-/- mice with colitis, while expression of IL-12 and iNOS is significantly compromised in ICSBP/IL-10 double KO mice. In agreement with these results, patients with CD have significantly higher ICSBP expression than normal individuals. ICSBP is active in several loci. ICSBP interacts with TRAF6 in the TLR4 pathway, and binds to ISRE sites in the iNOS and IL-12 p40 promoters, activating the expression of these genes. In addition, we find that ICSBP is ubiquitinated by the E3 ligase Cbl, resulting in its degradation by the proteasome. To expore ICSBP as a suitable target for therapy in CD, this proposal is structured around three aims: 1) We will analyze the regulation of ICSBP expression in macrophages and dendritic cells activated with various TLR and NOD2 ligands. In addition, we will define the role of ICSBP in the generation of regulatory T cells. 2) We will define the function of Cbl in the control of Thl immune immune response and analyze the role of Cbl in the development of colitis. 3) We will define the therapeutic effects of TLR4 and ICSBP inhibition by cell-permeable peptide reagent in vivo in murine colitis models. These studies will advance our understanding the role of ICSBP in the mucosal immune response, and may identify ICSBP as a new target for therapy in CD.